Studies on the Solvent Effect of Aquo-n-Propanol Solvent Systems on the Catalysed Solvolysis of Aliphatic Decanoate Ester

The solvent effect of a primary alcohol namely n-propanol on the alkali catalysed solvolysis of reaction was studied by carrying out the hydrolysis of the ester having longer carbon chain namely Methyl decanoate in water-n-propanol media of varying composition consisting of 30 to 80% n-propanol (v/v) at different temperatures ranging from 20 to 40°C. The specific rate constant values of the reaction were found to be depleted with increasing concentration of n-propanol in the reaction media. It was found that number of water molecules associated with the activated complex increases from 0.300 to 1.495 with increasing temperature from 20°C to 40°C and this tells about the fact that the bimolecular mechanistic path of the reaction is changed to unimolecular. The decrease and increase observed respectively in the values of iso-composition activation energy (EC) and iso-dielectric activation energy (ED) of the reaction show that the transition state is solvated and initial state is desolvated with addition of n-propanol in reaction media. From enhancement observed in values of ΔG* with simultaneous depletion in ΔH* and ΔS* values of the reaction, it has been concluded that the reaction is enthalpy stimulating and entropy inhibiting and specific solvation is taking place in the water-n-propanol media. From the evaluated values of iso-kinetic temperature, Le 284.80≈285 which is less than 300, it is inferred that this reaction in water-n-propanol media obeys BarclayButler rule and there is a weak but considerable solvent-solute interaction taking place in the reaction media.